Aluminum base bearing



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7 2,807,540 I ALUMINUM BASE BEARING Alfred W. Schluchter, Dearborn, Mic11., assignor to General Motors Corporation, Detroit, Mich., acorporation of Delaware 7 4 Claims. (Cl. 75-142) This'invention relatesto an aluminum base alloy and particularly 'to an improved alloy of thistype having properties rendering it especially suitable for use as abearing material.

Many aluminum base bearing alloys, such as the type disclosed in PatentNo. 2,238,399, which issued April 15, 1941, in the name of Alfred W.Schluchter, are satisfactory bearing materials in most respects.However, such alloys cannot be satisfactorily heat treated so as toprovide sufficient hardness for many purposes. Ac cordingly, a principalobject of my invention is to provide an aluminum base bearing alloywhich can be heat treated so that it possesses a hardness comparable tothat of any conventional hardenable aluminum alloy and which, at thesame time, can be rolled into strip form by conventional commercialmethods.

- A further object of this invention is to provide such a heat treatablealuminum alloy which has good score resistance when used as a bearing.Aluminum and most of its alloys are generally quite unsuitable for usein bearings for machine parts of iron for the additional reason thataluminum tends to adhere to, or combine with, the ferrous metal, therebycausing scoring or seizing. I have found, however, that by a suitablecombination of alloying constituents this difficulty can be overcome andan alloy produced having not only excellent anti-friction properties butother characteristics especially desirable in a bearing material.

In accordance with my invention, therefore, the foregoing and otherobjects and advantages are attained to a particularly high degree in analuminum base alloy con- 2,807,540 Patented Sept. 24, 1957 'ice having acorrespondingly longer fatigue'life. As a result of this hardness, solidbearings made from this alloy also retain their original shapes muchbetter than many of the bearings which heretofore have been made ofsofter alloys. The former do not take a set at temperatures to whichthey are normally subjected, and they undergo a negligible amount ofshrinkage when removed fromen raining copper, magnesium, cadmium andsilicon. Inasmuch as the alloy thus produced is a much stronger metalthan the aluminum alloys generally heretofore used for bearing purposes,solid bearings may be made from it, no backing of steel or similarmetals being necessary for many applications. Of course, this alloy canalso be readily bonded to steel and many other metals and can be used ona backing of such metals. Moreover, if desired, a bearing formed from myalloy may be advantageously provided with a thin'overlay of lead or alead base alloy. Examples of these overlays include the lead-tin andlead-indium alloys which are used for this purpose and in which the leadis the major C011, stituent. Hence it is obvious that, as wellrecognized by the trade, the term bearing is used herein as meaning anelement which performs a bearing function regardless of the presence orabsence of such an overlay.

gin'es after extensive use. Despite these aforementioned properties, thealloy can be easily rolled down by conventional methods.

In accordance with my invention, highly satisfactory bearing propertiesare obtained with an alloy having the following composition by weight:0.05% to 3.0% magnesium, 0.05% to 5.0% cadmium, 0.3% to 11.0% silicon,0.1% to 3.0% copper and the balance substantially all aluminum. Variousincidental impurities may be in cluded in this alloy in the usual smallamounts without any substantial detrimental effects. For example, iron,which together with silicon is present in commercial aluminum, may bepresent in amounts up to 0.5% without causing any harmful results. Undersevere test conditions, alloys having the above composition showexcellent anti-friction properties so that bearings formed of this alloynot only do not score or gall when in contact with a rotating steelshaft, but neither the shaft nor the bearings show an appreciable amountof Wear after long and severe use. I have also found that the resistanceof this alloy to cracking or crumbling is extraordinarily high.

The magnesium is added to increase the hardness of the bearing alloy, amagnesium content of only 0.05% being sufficient to provide a sufficientdegree of hardness for many applications. Inasmuch as the moltenmagnesium tends to oxidize during the alloying procedure, however, forbest results it is preferable that the magnesium be added in amountsequal to at least 0.2% of the weight of the alloy. 'Magnesium hasanadverse effect on score resistance and friction properties, however,and as a result the magnesium content should not be higher thanapproximately 3.0%.

With additions of magnesium in amounts greater than approximately 0.5%,the increase in hardness is relatively slight. Moreover, if themagnesium content is not higher than this amount, theaddition of coppertends to offset the adverse effect of magnesium on the score propertiesof the alloy. Accordingly, a magnesium content ranging from 0.2% to 0.5is preferred, approximately 0.5% magnesium generally being the optimumamount to be added. V

The addition'of cadmium greatly improves the score resistance of thealloy. Despite the fact that it has been generally recognized that theaddition of cadmium to aluminum causes slight loss of strength, I havefound that cadmium, in the presence of silicon, may be beneficiallyintroduced in amounts as large as 5.0% without causing a measurable lossof strength. 7 In fact, the resultant alloy is remarkably resistant todisintegration under impact or pounding such as occurs in severe bear-ting service. Moreover, thepresence. of cadmiurndocs not affect thehardness if the alloy issubsequently hmt treated. Although the effect ofcadmium on both strength and hardness is negligible in anyoevent ifadded in quantities no greater than 5.0%, cadmium is a relatively softmetal and hence the cadmium content should not be higher than thisamount. v

I have also found that a cadmium content greater than 5.0% tends tocause this element to segregate out and settle to the bottom of thecasting during the solidification thereof in the form of the apparentlynearly pure, metal. Thus, too high a cadmium content raises the cost ofthe alloy by increasing personnel expenses because of increased handlingcosts and the necessity, ofmore detailed andcareful' supervision.Moreover, inasmuch as cadmium is also a relatively expensive andsomewhat rare metal, it is desirable to add only as much of this metalas is necessary to produce the desired results.

There is a marked improvement 1 in score properties it cadmiumis addedin quantities up to 2.5%, but increasing the cadmium content beyond thisamount does. not an preciably increase the. score ,resistance of thealloy. Hence, cadmium preferably should be present in an amount rangingfrom approximately 0.2% to 2.5% in order to provide the most desirableanti-friction proper= ties. Inasmuch as cadmium also tends to volatilizeat the temperature of molten aluminum, however, it often may bedesirable to add slightly greater amounts of cadmium tooflsetlanylosses. due tothis tendency for volatilization. Arcadmiumcontentof at least 0.5% is necessary in all instancesto, provideadequate score resistance.

Theinclusion of silicon in my aluminum base bearing alloy alsoenhancesitsscore resistance. This property of silicon, plus the manner in whichit influences the effects of the cadmium present in the alloy and thefact that solidification shrinkage is lower as the silicon content is.raised, dictates that the alloy contain at least 0.3% silicon. Inasmuchas a high silicon content interferes with rolling processes,.however,the maximum amount of silicon. to be added necessarily is governed bythe method in which the article, such as a bearing, is formed.Accordingly, silicon. should not be present in amounts greater than 5.0%in the wrought alloy because such an alloy needs to be rolled, while itmay be added in amounts as high as 11.0% in the cast alloy. While anincreased I silicon content improves score resistance, the addition ofsilicon in amounts greater than 5.0% provides only slightadditionalbeneficial properties in this respect. Accordingly, .bestresults are obtained for most purposes when the siliconcontent is keptwithin a preferred range of 2.0% to 5.0%.

Theaddition of copper, in conjunction with the mag nesium present in thealuminum base alloy, contributes to the hardenability of the resultantalloy. The hardness of the alloy will be reduced to too great an extentif the copper content is below 0.1%, and the addition of at least 0.3copper is preferable in order to obtain a satisfactory degree ofhardness in those applications where this property is ofprimeimportance. Where even greater hardnesswis desired, amounts of copper ashigh as 3% may be added and, in the case of the cast alloy, the coppercontent may be as high as 5% in some instances. Copper should notbepresent in amounts greater than about 3% in the wrought alloy, however,because of the difficulties which would otherwise be encountered inrolling operations due to the reduction in .ductility of this alloy. Ingeneral, theincrease in the hardness of the alloy resulting from theaddition of copper in quantities above approximately1% is notsubstantial if this alloy is subsequently subjected to a suitable formof heat treatment, such as the preferred :one hereinafter described. Inthe absence of such a heat treatment, however, the hardness of the alloycontinues to increase with the use of the larger amounts of copper. Itis usually not feasible to add more than 3% copper because increasingthe copper content above this amount'raises alloy costs by greatlyincreasing the difficulty in casting and fabrication of the castparts.

As a result of. the above considerations, I have found that a coppercontent within a preferred range of 0.3% to 1% provides excellentresults in all respects.

In the alloy hereinbefore described, it is necessary that both magnesiumand copper be used in conjunction to obtain the desired hardness. Theuse of either one of these metals alone in a quantity equal to thecombined amounts of the two metals will not provide the same degree ofhardness as the use of the two metals'in combination.

1 The above alloy possesses the aforementioned desirable characteristicsto an outstanding degree when it consists by the absence of continuousnetworks of relatively brittle eutectic mixtures. Conventional alloyingprocedures may be employed with intermediate alloys, such asaluminumsilicon and aluminum-copper alloys, being used to introduce thesilicon and copper. It is desirable that the more volatile elements,such as cadmium, be the last to be added to the melt in order to preventtheir vaporization. In general, it is advisable to use the lowesttemperature possible to keep the cadmium from vaporizing. For example, Ihave found that the aluminum, silicon and copper mayadvantageously befused at a temperature in the order of approximately 1200 F., the meltthen preferably being removed from the furnace. The magnesiumand cadmiummay next be successively added to the melt, which is subsequentlystirred and cast, usually in metal or graphite molds. The highesttemperature suitable for casting is that point at which the cadmium justbegins to vaporize or smoke. and, in order to avoid loss of metal, it isdesirable not to raise the temperature of the melt above this point.Accordingly, care should be taken to prevent the temperature fromexceeding approximately 1400 F. The alloy may be either cast in thedesired form for use in hearings or it may be cast in ingots, rolleddown to strip material of the desired thickness, and bearing liners orother bearing elements formed from the stock.

Cast articles having a metallographic structure showing a'continuousnetwork of segregated metal compounds may be improved as to strength andfatigue resistance by suitable heat treatment. For example, I have foundthat a solution treatment at a temperature between approximately 900 F.and 1050 F. for a period of eight to fifteen hours is particularlyeffective to more completely dissolve the constituent elements and forma solid solution. Upon removing the alloy from the furnace following thesolution treatment, it is preferable to cool it immediately by quenchingin water. This treatment provides the alloy with the high degree ofductility, such as is desirable for rolling operations; and it may thenbe easily rolled down to strip material of the desired thickness.

A precipitation treatment may: thereafter be employed to substantiallyincrease the hardness of the alloy. This process is preferably carriedout by heating the article for five to ten hours at a temperature in therange between approximately 300 F. and 400 F., a precipitation treatment at 370 F. for eight hours being particularly satisfactory. Thealloy then may be again cooled, preferably in water, and suitablymachined. Such a heat treating process results in an article which isthree or four times as hard as it. was in the as-cast condition andwhose fatigue strength is proportionally improved. 7 The specificgravity of the above-described alloy is about one-third that of atin-bronze bearing alloy, and has much greater resistance to fatigue orto cracking under the pounding action to which bearings, such asconnecting rod bearings, are subjected. This property renders such analloy particularly suitable as a bearing for use underextremeconditions, tests on such bearings indicating the remarkableabsence of wear, either of the hearing or the shaft. In addition, thealloy appears to be resistant to corrosion by acid constituents oflubricatingoils which attack many other bearing compositions.

It is to be understood that, while the invention has been described inconjunction with certain specific examples, the scope of the inventionis not to be limited thereby except as defined in the appended claims.

I claim:

1. A bearing formed from a heat-treatable wrought alloy consisting of0.05% to 3% magnesium, 0.05% to 5% cadmium, 0.3% to 5% silicon, 0.1% to1% copper, and the balance aluminum plus incidental impurities.

2. A bearing formed of an alloy consisting essentially of 0.05% to 3%magnesium, 0.05% to 5% cadmium,

0.3% to 11% silicon, 0.1% to 5% copper, to 0.5%

iron, and the balance aluminum.

3. A bearing characterized by high anti-friction properties andresistance to distintegration under impact and to attack by acidsdeveloped in lubricating oils, said bearing being formed of an alloyconsisting of 0.05 to 3% magnesium, 0.05 to cadmium, 0.3% to 5% silicon,0.1% to 3% copper, and the balance aluminum plus incidental impurities.

4. A bearing formed of an alloy capable of being rolled into sheet formfrom cast ingots and having high antifriction properties and fatigueresistance, said alloy consisting essential of 0.2% to 0.5% magnesium,0.2% to 2.5% cadmium, 2% to 5% silicon, 0.3% to 1% copper, iron not inexcess of 0.5 and the balance aluminum.

References Cited in the file of this patent UNITED STATES PATENTS1,079,035 Tebbetts Nov. 18, 1913 1,333,337 Pack et a1. Mar. 9, 19201,508,556 Jefr'ries et al. Sept. 16, 1924 1,572,487 Jeifries et a1. Feb.9, 1926 1,945,297 Sterner-Rainer Jan. 30, 1934 2,026,559 Kempf et a1.Jan. 7, 1936 2,026,561 Kempf et al. Jan. 7, 1936 2,026,571 Kempf Jan. 7,1936 2,076,281 Steudel et a1 Apr. 6, 1937 2,122,535 Nock July 5, 19382,214,432 Murphy et a1 Sept. 10, 1940 2,225,925 Nock Dec. 24, 19402,238,399 Schluchter Apr. 15, 1941 2,263,823 Bonsack Nov. 25, 19412,277,023 Steiner Mar. 17, 1942 2,352,990 Wood July 4, 1944 2,357,578Brownback Sept. 5, 1944 2,435,991 Whitfield Feb. 17, 1948 2,501,440 DixMar. 21, 1950 2,586,099 Schultz Feb. 19, 1952 2,599,726 Schluchter June10, 1952 FOREIGN PATENTS 534,623 Great Britain Mar. 12, 1941 550,516Great Britain Jan. 12, 1943 OTHER REFERENCES Metal Handbook, 1948edition, pub. by Amer. Soc. for Metals, p. 776.

Ser. No. 327,066, Garre (A. P. C.), published May Norton et a1 July 16,1889 4, 1943,

4. A BEARING FORMED OF AN ALLOY CAPABLE OF BEING ROLLED INTO SHEET FORMFROM CAST INGOTS AND HAVING HIGH ANTIFRICTION PROPERTIES AND FATIGUERESISTANCE, SAID ALLOY CONSISTING ESSENTIAL OF 0.2% TO 0.5% MAGNESIUM,0.2% TO 2.5% CADMIUM, 2% TO 5% SILICON, 0.3% TO 1% COPPER, IRON NOT INEXCESS OF 0.5%, AND THE BALANCE ALUMINUM.